His comments came after another mother had an emergency birth in Lumsden yesterday, delivering her child in the Lumsden maternal and child hub car park about 1am.
It is the third emergency birth since the Lumsden Maternity Centre was downgraded in April.
In May, Amanda McIvor gave birth to baby Levi in the back of an ambulance near Lumsden, and earlier this month, another mother gave birth at the hub.
Mr Walker believed if the maternity centre had not been downgraded, a second midwife would have been on site and that would have "drastically improved" the chances of the mother making it inside the facility, to deliver her fourth child.
Further, because there were no postnatal care facilities in Lumsden, the woman was discharged and sent home within a couple of hours.
"She couldn't afford to go to the nearest postnatal primary birthing unit, over 75 minutes away from her home, so she was discharged back to the farm.
"She's got three other kids, one with a medical condition, and her farm is where her community support networks are.
"Had Lumsden been open, she could have spent a couple of days there, only 15 to 20 minutes from her home."
He said that flew in the face of the "wellbeing Government", and despite asking Ms Ardern to intervene, she had "completely ignored us".
"What's it going to take before they finally listen and stop putting the lives of rural Southland mums and babies at risk?
"It's incredibly disappointing in 2019 we've got a `wellbeing' Prime Minister who's forcing mothers to give birth without making it to a primary birthing unit.
Mr Walker said he had spoken to the new mother and she and her baby were "doing fine".
Southern DHB chief executive Chris Fleming said in a statement he did not yet have all the details, but was "pleased the midwife was able to use the facility to support the mother and baby following this event" and congratulated the family on the new arrival.
"Southern DHB is a large geographical area and some births do happen quickly.
"This is why we have reorganised maternity services across the district so we can increase the equipment and support for midwives in more locations, including establishing hubs in Te Anau and Wanaka, where there was previously no formal maternity infrastructure.
"This means there are now more locations across Otago and Southland where rapid births can be better supported."
The DHB announced it was downgrading the Lumsden centre in August, meaning babies would be delivered there only in emergencies.
In November, Mr Walker submitted a petition to the Health Select Committee asking for that decision to be reversed.
The committee was to have announced this week if it would investigate the DHB's decision, but has delayed that until Wednesday.
